Storm water systems are generally designed to provide adequate dewatering of surface areas while addressing related issues such as protection of watershed water quality, erosion, etc. Integral within any system plan or design is an assessment of the topography of the site for grading within the area of concern. Of course, regions of consistently flat topographies, such as the low-lying areas of the city of New Orleans, provide particular challenges to storm water removal. In such topographies, pumping stations may be required for dewatering, transporting water both horizontally and vertically.
In situations where a dewatering system is responsible for large surface areas, the associated pumping systems must be capable of pumping large volumes of fluid. Such larger systems typically require robust pumping stations having sizable pumps, motors, power supplies, supporting piping, and other equipment. Such pumping stations have been used in a variety of circumstances, such as the evacuation of seepage from low elevation areas, removal of storm drainage, transfer of sewage, maintenance of canal systems, etc. Some pumping stations may be temporarily installed for the pumping of mines or deep wells. Somewhat similar dewatering systems may be found on ships, sometimes using bilge pumps with catch basins, and other times as a bilge evacuation or fire main eductor system.
In general, there are two types of pumping stations seen in civil infrastructures: wet-pit and dry-pit. In a wet-pit station, submersible pumps are immersed in water contained within a sump or wet well. Submersible pumps have been generally preferred for storm water removal. Dry pit stations provide both a wet well and a dry well. The wet well stores the water to be pumped, which is transferred to the dry well by piping. The two stage process of dry pit stations make them more expensive, but enables maintenance of the pump without removal from the wet well. The pumps conventionally used in these stations may be classified by the type of flow, such as axial flow, radial flow, or mixed flow. The type of flow indicates the type of device used to impart energy to the water. Axial flow pumps typical use propellers to create a low pressure or head with a high volume flow in the direction of the propeller axis. Radial flow pumps typically use impellers to create a high pressure or head with a centrifugal flow about the axis of the impeller. Mixed flow pumps use a combination of the above two types of flow. Each of these types of pumps requires a motor to drive the propeller or impeller through an axle or drive shaft.
Of course, both of the above approaches involves considerable infrastructure. Another hazard that the conventional pumping systems face is the presence of sediment, debris, sand, or other such objects within the fluid to be pumped. Sediment can damage a pump propeller or impeller. Most pumps stations require a significant filtering system to clean the fluid prior to it being pumped. However, filters increase the resistance to flow, causing the pump to work harder and the motor to consume greater power for the volumetric flow pumped. In some cases, filters may become clogged. In general, conventional pumps may require additional maintenance and expense of operation when used in an unclean environment. Unfortunately, an unclean environment is typical for most dewatering systems. Filters and grates designed to protect pumps are common problems for dewatering systems.
Another aspect is the need for the supporting systems of a pumping system. Most conventional pumping systems require an ongoing supply of power to maintain operation of the motors driving the pumps. Even eductors require a minimum level of fire main pressure and flow in order to generate a vacuum at the intake port of the eductor. Yet in the conditions requiring dewatering, such as flooding caused by storms, or a flooding casualty aboard ship, the power supply may be unreliable.
Some other approaches to pumping fluids have involved the use of air lift pumps or equivalent structures. Air lift pumps commonly create a multiphase mixture of gas and fluid within a vertical pipe, the mixture having a lower density than the surrounding fluid. The difference in density can induce the mixture to travel up the vertical pipe and ultimately to discharge. Other efforts involve creating a pressure differential between vessels in a closed system to move fluid from a high pressure vessel to a lower pressure vessel. These structures are not well adapted to the environments common in large volume, open system dewatering, with large surface areas, debris laden water, the need for horizontal transport, reliability, independent power sources, etc. Conventional air lift pumps require inlets placed at considerable depth below the water surface and function primarily in the vertical so that the multiphase mixture will be sustained as it rises. Further, air lift pumps are generally inefficient and closed pressure vessel systems are expensive and complicated.
Accordingly, it would be useful to have a dewatering system that is capable of handling a large volume of fluid, capable of pumping fluid contaminated with sediment, and capable of operating without a dedicated motor with available power.